Proximity sensors have been used to sense the proximity of fingers, styluses, hands, and other objects. Proximity sensors can be used as non-touch input interfaces. Non-touch input interfaces can be helpful with numerous software applications such as free-finger key entry, free-finger gesturing or handwriting, navigation, and manual manipulation of software objects, to name a few. Proximity sensors can have practical advantages; they can enable efficient interaction on small devices that have small input areas, they can avoid the mechanical wear and tear of contact type input devices, they are unobtrusive, and they can be used for both touch and non-touch input.
A variety of types of proximity sensors have been used. Acoustic sensors, while feasible, can be affected by echoes, air currents, and humidity. Optical sensors operate by line-of-sight, require significant power, can be affected by surface texture, have a slow update rate, and involve expensive post-processing to make sensing decisions. Capacitive proximity sensors, also known as electric field sensors, are also available, but they have had low range and sensitivity, and their size has been dependent on the size of sensor electrodes.
Devices and techniques discussed below relate to capacitive based proximity sensing that may result in improved range and sensitivity in the presence of a finger or other conductive object, while possibly allowing miniaturization and low power consumption.